Controllable construction of core-shell CuCo₂S₄@polypyrrole nanocomposites as advanced anode materials for high-performance sodium ion half/full batteries

It is important to design and fabricate novel anode materials with stable structure and high capacity for sodium ion batteries (SIBs). Herein, core-shell CuCo2S4@polypyrrole (CS-CuCo2S4@PPy) nanocomposites were prepared by a facile solvothermal reaction and subsequent in situ chemical oxidation polymerization. The CS-CuCo2S4@PPy nanocomposites show superior electrochemical performance for half SIBs with a high reversible capacity (551.2 mA h g-1 at 0.1 A g-1 after 200 cycles), excellent rate capability (370.7 mA h g-1 at 2 A g-1), and ultra-long cycling stability (324.9 mA h g-1 at 2 A g-1 after 2000 cycles). In addition, the kinetic analysis reveals that 74.6% of charge contribution is from capacitive-controlled capacity. The Na3V2(PO4)3‖CS-CuCo2S4@PPy full cell further illustrates its practical application with a high capacity of 243.6 mA h g-1 at 0.5 A g-1 after 150 cycles. The competitive electrochemical performances of CS-CuCo2S4@PPy can be attributed to the core-shell structure and the synergistic effect of CuCo2S4 and PPy. The ternary spinel CuCo2S4 can offer rich valence constituent and active sites to achieve high capacity. The PPy layer cannot only improve the electrical conductivity but also buffer the volume variation to protect CuCo2S4 spheres from pulverization during the charge/discharge processes. This work provides a facile method to prepare conductive polymer-coated transition metal sulfide nanocomposites with stable core-shell architectures, confirming their potential application in the energy storage and conversion field.